The missing link to Penny's (Kaley Cuoco) past will be finally revealed in season 10 of "The Big Bang Theory."

During the 2016 San Diego Comic Con panel, showrunner Steve Molaro revealed that "Sons of Anarchy" star Katey Sagal will portray the role of Penny's mother Susan, while "30 Rock" alum Jack McBrayer will portray the role of Randall, Penny's brother.

According to CBS, Penny's mother is already stressed out and already anxious because of living with a troubled son. Meanwhile, Randall is described as a "cheerful former drug dealer and ex-con." The two might cause trouble when they visit Penny and her husband, Leonard (Johnny Galecki).

In an interview with TVLine's Michael Ausiello during the 2016 SDCC, Molaro and co-producer Bill Prady revealed that Sagal had been previously considered to play a different role in the series, but it did not work out. But when she was asked to portray the role of Susan in the series, the actress agreed right away.

When asked when Penny's family will arrive in the series, Molaro said at the panel, as reported by Variety: "The season premiere will be picking up the night after the final episode of season 9, so we left it at Penny and Leonard were gonna do a re-do wedding for their family and friends 'coz they eloped. So they are coming to town for this re-do wedding. And along with Penny's mom is Penny's brother who over the years we have head has been in and out of jail."

The showrunner also revealed what to look forward to in Penny's possible career for the upcoming season. "We're still figuring things out; I think she's in an interesting and relatable place. She's going to start to weigh her options," he stated.

The upcoming season is also expected to discuss what's next for Sheldon (Jim Parsons) and Amy's (Mayim Bialik) relationship, especially after the two decided to be physically intimate in season 9.

"The Big Bang Theory" season 10 will premiere on CBS on Monday, Sept. 19.